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Old 21st October 2006, 11:09 PM   #1
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Post AudioSector LM4780 Dual-Mono - questions/build log

Hi all!

I'm still very new to this stuff. I built a CMoy headphone amp thanks to this excellent tutorial and had a lot of fun with the project, so I've decided to bite off more than I can chew and start a project like this.

It's also the first time I've dealt with AC voltages outside of a circuit analysis lab at school, so I'm doing lots of research and will be asking plenty of questions before I break out the soldering iron.

I've ordered the LM4780 PCB from AudioSector.com (looks great!) and have slowly been sourcing some parts. My intention is to have one chip (in parallel configuration) per channel, both in one chassis, and I'd like to keep the dual-mono design right down to the transformers. I may also include a stepped attenuator. We'll see.

The amplifier sections shouldn't be too difficult to build thanks to Peter Daniel's excellent work, but I'm a little uncertain about the power supply so I'll post up what I had in mind for comments and criticism, as I'd like to put off any serious cases of death.

Click the image to open in full size.

Salient issues (so far):

1) I'm a little uncertain about fuse placement in the circuit. I read that they should be slow-blow and 3.15A for 115/120V mains. I think I may have them on the wrong wire now that I look at the schematic.

2) The recommended transformer rating is 300VA, 22V+22V for one chip; will I have trouble using two for two chips, wired in parallel with the mains? I'm thinking of going with Plitron Standard series trafos.

3) The recommendation for the rectifier diodes is the MUR860; Digikey only seems to stock the lead-free variant, the MUR860G. Will this cause problems / sound quality deterioration?

4) The 1000uF caps will likely be 50V Black Gates. Apparently there's no need for snubberizerationification (or whatever the technical term is).

Please go ahead and tear this apart so's I don't blow myself up!


-A
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Old 22nd October 2006, 02:08 AM   #2
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hi gongzero,

I would normally only use a single fuse in the active/live AC wire. The rating would have to be changed accordingly. You can get an IEC chassis male socket with a fuse holder built in. This will simplify the construction process and reduce the chance of an wiring error.

regards
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Old 22nd October 2006, 04:38 AM   #3
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Why dont you just get the parts kit for the board from Peter?

I have built 3 dual mono kits from him and the parts he supplies is great stuff.

Dominick
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Old 22nd October 2006, 03:43 PM   #4
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Quote:
Originally posted by Greg Erskine
hi gongzero,

I would normally only use a single fuse in the active/live AC wire. The rating would have to be changed accordingly. You can get an IEC chassis male socket with a fuse holder built in. This will simplify the construction process and reduce the chance of an wiring error.

regards
Greg, that's an excellent idea. Part of the fun of building something is finding out that parts like this exist!


Quote:
Originally posted by Dominick22
Why dont you just get the parts kit for the board from Peter?

I have built 3 dual mono kits from him and the parts he supplies is great stuff.

Dominick
I don't doubt the quality of the parts!

Mostly the issue was myself being a poor student and only being able to buy parts $30-40 at a time.

I am using his application notes to guide my purchases, though.


-A
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